1. Field of the Invention
The invention relates to the field of locking devices for windows and in particular to a locking device which allows a cranked window to be opened for ventilation but prevents forced entry.
2. Description of the Prior Art
One of the popular historical designs for metal windows includes a window that is hinged on a side and cranked open and shut by a hand cranked gear mechanism provided at the base of the window interior to the dwelling or structure. A crank handle is rotated either clockwise or counterclockwise to drive a conventional gear mechanism which rotates the window on its hinge. There is sufficient mechanical advantage in the gear mechanism such that only a small amount of cranking force is required to rotate the window open and shut, even if there is substantial friction or drag in the rotation of the window. Furthermore, the mechanical advantage is great enough that the gear mechanism acts as a locking device for the window. Under ordinary circumstances the window cannot be pried open to any significant extent, because of the locking action provided by the high gear ratio of the mechanism. Therefore many owners simply rely on this mechanical advantage as the sole lock on the windows notwithstanding that a separate locking latch may be provided.
However, while the gear mechanism cannot be turned by normal forces applied to the window, someone attempting to make forced entry through such a window can do so by using a crowbar or similar tool to apply an excessive force to the gear mechanism such that the gear teeth are simply stripped or the gears themselves broken. The mechanical latch, even when used, can also be forced or broken by such excessive forces. Once the gear mechanism and latch are stripped or broken, the window can often then be easily opened and entry obtained.
While a large number of conventional locking mechanism can be used to provide additional security for such windows, such mechanisms typically require the window to be shut in order to be engaged. The particular advantage of these windows, namely that they can be rotated open and shut by varying amounts to provide desired ventilation, is thereby defeated when such additional latches or locking mechanisms are employed.
Therefore what is needed is a simple, and inexpensive mechanism which can be retrofitted to cranked windows without the requirements of special tools or skills, which provide a high degree of security similar to that provided by conventional latching mechanisms, but which do not prevent operation of the window for purposes of providing ventilation.